Electrical winding with interleaved conductors

ABSTRACT

An electrical winding having a plurality of pancake coils of the interleaved turn, high-series capacitance type. Each pancake coil has first and second radially interleaved coil sections, each of which are severed to provide first and second radial portions. The radial portions of the pancake coils are interconnected to provide a plurality of basic pairs, and the adjacent coils of adjacent basic pairs are interconnected, to provide first and second electrical paths or circuits through the winding. The interleaving arrangement directs the electrical paths inwardly in the first pancake coil of the basic pair, with the turns of the two paths being mutually interleaved, and outwardly in the second coil of the basic pair, with the turns of the two paths each being self-interleaved.

United States Patent 3,299,385 1/1967 Stein 3,391,364 7/1968 Steinetal.

ABSTRACT: An electrical winding having a plurality of pancake coils of the interleaved turn, high-series capacitance type. Each pancake coil has first and second radially interleaved coil sections, each of which are severed to provide first and second radial portions. The radial portions of the pancake coils are interconnected to provide a plurality of basic pairs, and the adjacent coils of adjacent basic pairs are interconnected, to provide first and second electrical paths or circuits through the winding. The interleaving arrangement directs the electrical paths inwardly in the first pancake coil of the basic pair, with the turns of the two paths being mutually interleaved, and outwardly in the second coil of the basic pair. with the turns of the two paths each being self-interleaved.

I MUTUALLY INTERLEAVED SELF INTERLEAVED ELECTRICAL WINDING WITI-I INTERLEAVED CONDUCTORS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates in general to electrical inductive apparatus, such-as power transformers, and more particularly to windings for such apparatus.

2. Description of the Prior Art The electrical windings of certain types of electrical inductive apparatus, such as power transformers, are formed of a plurality of pancake-type coils disposed in spaced side-by-side relation, and electrically connected to form a winding. In order to more uniformly distribute surge potentials across such a winding, each pancake coil may have a plurality of sections, the turns of which are radially interleaved with one another, and the sections interconnected to place turns from an electrically distant portion of the coil or winding between electrically connected turns. This method of constructing a pancake coil or winding to increase its through or series capacitance is termed interleaving.

There are many different known interleaving arrangements, which provide difierent degrees of interleaving, and thus different values of effective series capacitance. The specific arrangement selected for a winding will depend upon the specific application. The interleaving arrangements commonly used complete the basic interleaving pattern in one pancake coil, or it completes two basic interleaving patterns in one pancake coil, or it requires two pancake coils to complete one basic interleaving pattern, referred to a single, double and twin interleaving, respectively. The interleaving arrangements are further identified as either being self-interleaved, where the voltage difference between the turns is achieved by interleaving turns from the same circuit or path through the winding, and mutual interleaving where two or more parallel connected conductors are interleaved with one another to obtain the voltage difl'erence desired between adjacent turns.

When current requirements of an application are such that two parallel conductors are required, it is common to use a twin, mutually interleaved arrangement, such as disclosed in US. Pat. No. 3,260,978. These arrangements disclose a winding having two parallel paths, in which the pancake coils are connected in basic pairs, and the basic pairs are interconnected to complete the winding. While the interleaving arrangements disclosed in this patent provide excellent windings, having a voltage difference between adjacent turns in each pancake coil equal to one unit of voltage, where one unit is the voltage across one coil section of a pancake coil, it would be desireable, at least in certain applications, to be able to reduce the voltage stress in the duct space between adjacent coils of adjacent basic pairs of coils, compared with certain prior art arrangements. The reduction in duct stress, however, should not be accompanied by a change in the tum-totum voltage, as this would then change the effective series capacitance of the structure.

SUMMARY OF THE INVENTION Briefly, the present invention is a new and improved winding for electrical inductive apparatus having a plurality of pancake coils. Each of the pancake coils have first and second coil sections, and each coil section is divided into first and second radial portions. The radial portions of adjacent pairs of pancake coils are interconnected to provide a plurality of basic pairs of coils, which embody one complete interleaving arrangement having two separate electrical paths, and adjacent coils of adjacent basic pairs of coils are interconnected to continue the two separate electrical paths throughout the winding. The coil-to-coil or duct stress between the pancake coils of adjacent basic pairs is reduced to two voltage units, by an interleaving arrangement in which the turns of the two electrical paths are mutually interleaved and spiral inwardly in the first coil of the basic pair, and the turns of the two paths are each self-interleaved and spiral outwardly in the second coil of the basic pair.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of the invention will become more apparent when considered in view of the following detailed description of exemplary embodiments thereof, taken with the accompanying drawings, in which:

FIG. 1 is a partial sectional elevation of a transformer having a winding constructed according to the teachings of the invention; and

FIG. 2 is a schematic diagram of the winding shownin FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, and FIG. 1 in particular, there is shown a partial sectional elevation of a magnetic corewinding assembly 12 of a transformer 10 constructed according to the teachings of the invention. The magnetic core-winding assembly 12 includes highand low-voltage windings l4 and 16, respectively, concentrically disposed about a leg 18 of a magnetic core assembly 20, in what is commonly referred to as core-form construction. Transformer 10 may be either single or polyphase, with only one base being illustrated in order to simplify the drawings. Transfonner 10 may be of the isolated winding type, with each end of the high-voltage winding 14 being adapted for connection to a source of electrical potential, or one end may be adapted for connection to ground, depending upon the particular requirements of the application. Transformer 10 may also be of the autotransformer type, if desired. The highand low-voltage windings l4 and 16, respectively are concentrically or coaxially disposed relative to an axis or centerline 22, with the windings only being shown on one side of centerline 22 as their views on the other side would be similar.

Low-voltage winding 16 may be of any conventional construction, having a plurality of conductor turns 24 which are insulated from the magnetic core 20 of high-voltage winding 14 by insulating means 26.

High-voltage winding 14 includes a plurality of pancake or disc-type coil sections of which pancake coils 28, 30, 32 and 34 are shown adjacent line terminal Ll. It is to be understood that the invention applies to any plurality of pancake coils, with each pancake coil having any desired number of conductor turns.

In general, each of the pancake coils, such as pancake coil 28, includes a plurality of conductor turns wound to provide an opening for receiving winding leg 18 of magnetic core 20 and low-voltage winding 16, forming a substantially disc shape having first and second outer major opposed surfaces and a predetermined radial build or outside diameter. The various pancake coils are stacked with their openings in alignment, with their major surfaces in spaced parallel relation with one another to form cooling ducts between the adjacent coils, such as cooling duct 36 between pancake coils 28 and 30, and cooling duct 38 between pancake coils 30 and 32.

The magnetic core-winding assembly 12 may be disposed in a suitable casing or tank (not shown), which may be filled to a predetermined level with a fluid insulating and cooling medium, such as oil or SF While in practice, the pancake coils of winding 14 may be constructed by a different method, it is convenient to describe them as being formed to first and second radially disposed insulated conductive strands spirally wound together to provide first and second coil sections, referenced I and II, respectively, in the schematic diagram of winding 14 in FIG. 2. Each of the conductive strands is severed" or divided at substantially its midpoint, also best shown in FIG. 2, to first and second radial portions in each coil section, with each of the radial portions having inner and outer ends, referenced from the axis 22 of the pancake coils. For example, coil section I of pancake coil 28 has first and second radial portions 29 and 31, respectively,

and coil section II of pancake coil 28 has first and second radial portions 33 and 35, respectively. Coil section I of pancake coil 30 has first and second radial portions 37 and 39, respectively, and coil section ll of pancake coil 30 has first and second radial portions 41 and 43, respectively.

Winding 14 has first and second circuits or paths, referenced the A and B circuits, which circuits are connected in common, at least at each end of the winding, to provide first and second parallel paths through the winding structure.

Winding 14 has its pancake coils connected, according to the teachings of the invention, in a plurality of basic pairs of pancake coils, and the coils of adjacent pairs of pancake coils are interconnected. Thus, it will only be necessary to describe the interconnection of two coils of a basic pair, as the remaining basic pairs are similarly connected and interleaved.

The first basic pair, comprising pancake coils 28 and 30, are interconnected such that the turns of the first and second electrical paths therethrough are mutually interleaved in the first coil 28 of the pair, with the paths spiralling inwardly in a first circumferential direction, and the turns of the first and second paths are each self-interleaved in the second pancake coil 30 of the pair, with the paths spiralling outwardly in the same circumferential direction as the paths in the first pancake coil 28. This mixing" of mutual and self-interleaving in the basic pair provides a winding structure in which the maximum voltage stress between adjacent pancake coils is two voltage units, where a voltage unit is the voltage across one coil section. This is a substantial reduction from prior art two conductor twininterleaved winding arrangements, where three and four voltage units between certain pancake coils of a structure is common.

More specifically, pancake coils 28 and 30 are interconnected to provide a basic pair of first and second pancake coils, respectively, by interconnecting the outer ends of the second radial portions 35 and 43 of their second coil sections, via conductor 40, the inner ends of the second radial portions 35 and 39 of the second and first coil sections of the first and second pancake coils, respectively, via conductor 42, the inner ends of the second and first radial portions 31 and 37 of the first sections of the first and second pancake coils, via conductor 44, the outer ends of the first radial portions 33 and 37 of the second and first sections of the first and second pancake coils, respectively, via conductor 46, the inner ends of the first radial portions 33 and 41 of the second sections of the first and second pancake coils, via conductor 48, and the inner ends of the first and second radial portions 29 and 43 of the first and second coil sections of the first and second pancake coils, respectively, via conductor 50.

The A and B circuits or paths through winding 14 are connected in common at the line terminal L1 and at the other end of the winding, and also at any tap connection points which may be included. The A circuit enters the outer end of the second radial portion 31 of the first coil section of pancake coil 28, via conductor 52, and spirals inwardly, as indicated by arrow 54, appearing at every other turn referenced with the letter A and a number which denotes the turn number from the start of the circuit in that particular basic pair. At the inner end of radial portion 31, the A circuit proceeds, via conductor 44, to the inner end of the first radial portion 37 of the first coil section of pancake coil 30, and spirals outwardly, as indicated by arrow 56, appearing at every other turn, until reaching the outer end of portion 37. The A circuit then proceeds via conductor 46 to the outer end of the first radial portion 33 of the second coil section of pancake coil 28, and spirals inwardly, appearing at every other turn. At the inner end of portion 33, the circuit proceeds via conductor 48 to the inner end of the first radial portion 41 of the second coil section of pancake coil 30, and spirals outwardly to the end of section 41. This completes the A circuit in the first basic interleaved pair, comprising pancake coils 28 and 30.

The B circuit enters the outer end of the first radial portion 29 of the first coil section of pancake coil 28, via conductor 58, and spirals inwardly, appearing at every other turn. THe B circuit is identified with the letter B and a number which indicates the turn position from the start of the B circuit in the basic pair. At the inner end of portion 29, the B circuit proceeds, via conductor 50, to the inner end of the second radial portion 43 of the second coil section of pancake coil 30. The B circuit spirals outwardly through portion 43 appearing at every other turn, and at the outer end of portion 43 it enters the outer end of the second radial portion 35 of the second coil section of pancake coil 28, via conductor 40. The B circuit spirals inwardly through portion 35, appearing at every other turn, and at the inner end thereof it proceeds, via conductor 42, to the inner end of the second radial portion 39 of the first coil section of pancake coil 30. The B circuit spirals outwardly through portion 39, and upon reaching the outer end of portion 39, the B circuit is completed in the first basic pair.

The second basic pair, comprising pancake coils 32 and 34, and all remaining pairs of pancake coils of the winding, are interconnected as hereinbefore described for the first basic pair, with like interconnecting conductors between the pancake coils of the first and second basic pairs, and like coil sections, being given like reference numerals with the addition of a prime mark in the second basic pair.

The interconnections between basic pairs is preferably accomplished in a manner which exchanges the relative positions of the A and B circuits or paths, from basic pair to basic pair. This arrangement has the advantages of: (a) keeping the inner pancake connection between basic pairs as short as possible, (b) providing a transposition of the A and B circuits from pair to pair, which reduces losses due to circulating currents, and (0) less stress is built up between pancake coils of adjacent pairs under surge voltage conditions. Accordingly, instead of directing the A circuit from the end of radial portion 41 to the outer end of the second radial portion of the first coil section of pancake coil 32, it is directed, via conductor 60, to the outer end of the first radial portion of the first coil section 29' of pancake coil 32. Thus the B circuit will then enter the outer end of the second radial portion of the first coil section 31 of pancake coil 32, via conductor 62.

The twin-interleaving arrangement disclosed herein mutually interleaves the turns of the two circuits or paths in the first pancake coil of the basic pair, i.e., the pancake coil in which the circuits spiral inwardly, while the turns of each path are self-interleaved in the second coil of the basic pair, i.e., the pancake coil in which the circuits spiral outwardly. More specifically, the turns of the A and B paths are interleaved in both the first and second radial portions of pancake coil 28, while in pancake coil 30, the turns in both of the first radial portions 37 and 41 are from the A circuit, and the turns in both of the second radial portions 39 and 43 are from the B circuit, resulting in self-interleaving of the two paths in this pancake coil.

This mixing of mutual and self-interleaving of the two parallel circuits in the coils of a basic pair, results in a reduction of the stress in the duct space between pancake coils of adjacent basic pairs, such as between pancake coils 30 and 32, and this reduction is achieved without affecting the voltage difference between adjacent turns within a pancake coil. The stresses between adjacent pancake coils, and between adjacent turns within a pancake coil, may be readily observed in the schematic diagram of FIG. 1 shown in FIG. 2, with the voltage stresses in units being listed adjacent the ends of the various radial portions of the coil sections. The unit voltage is listed at zero at the start of the A circuit, at the outer end of portion 31, it picks up one-half unit across portion 3|, it adds another one-half unit, making a total of one, at the outer end of portion 37, and the A circuit continues through the winding, picking up one-half unit as it traverses each radial portion of a coil section. The unit voltages are also listed for the B circuit, as the B circuit progresses through the winding. It will be noted that the difference in voltage between like radial positions of interleaved radial portions of a pancake coil is one unit, while the maximum voltage difference between pancake coils occurs between pancake coils 30 and 32, which difference is three units. This maximum voltage between adjacent pancake coils of three units is lower than the maximum voltage between adjacent coils of certain prior art twin interleaved two conductor windings.

in summary, there has been disclosed a new and improved high series capacitance, twin-interleaved winding for electrical power transformers, having two parallel connected paths therethrough. The winding has a plurality of pancake coils interconnected in basic pairs, and the basic pairs are interconnected, with each basic pair being connected to utilize mutual interleaving of the two circuits or paths in the first coil of the pair, and self-interleaving of each of the two circuits in the second coil of the basic pair. This arrangement reduces the maximum steady state stress between the pancake coils of adjacent basic pairs, compared with certain two conductor twininterleaved winding arrangements of the prior art, while maintaining substantially the same effective series or through capacitance of the winding, as obtained in the prior art structure.

I claim as my invention: 1. An interleaved turn, high series capacitance winding for electrical inductive apparatus, comprising:

a plurality of pancake coils disposed in spaced, side-by-side relation, each of said pancake coils including first and second insulated conductive strands spirally wound together to provide first and second radially interleaved coil sections, the first and second coil sections of each of said pancake coils each being severed to provide first and second radial portions, each having inner and outer radially spaced ends, first means interconnecting said plurality of pancake coils into a plurality of basic pairs, having first and second paths through each basic pair, with the paths spiralling inwardly in a first circumferential direction in the first coil of a basic pair, and outwardly in the same circumferential direction in the second coil of a basic pair, said first means interconnecting the coils of a basic pair such that the turns of the first and second paths are mutually interleaved in the first coil, and the turns of the first and second paths are each self-interleaved in the second coil of the basic pair,

and second means interconnecting the paths of the adjacent basic pairs to continue the first and second paths through the winding.

2. The winding of claim 1 wherein the second means interconnects the adjacent basic pairs such that the relative positions of the first and second paths are interchanged from basic pair to basic pair.

3. The winding of claim 1 wherein the first and second paths through the winding are interconnected, at least at the ends of the winding.

4. The winding of claim 1 wherein the first means interconnects, in each basic pair,

a. the outer ends of the second radial portions of the second coil sections of the first and second pancake coils,

b. the inner ends of the second radial portions of the second and first coil sections of the first and second pancake coils, respectively,

0. the inner ends of the second and first radial portions of the first section of the first and second pancake coils, respectively,

d. the outer ends of the first radial portions of the second and first sections of the first and second pancake coils, respectively,

e. the inner ends of the first radial portions of the second sections of the first and second pancake coils, and

f. the inner ends of the first and second radial portions of the first and second coil sections of the first and second pancake coils, respectively.

5. The winding of claim 4 wherein the second means interconnects adjacent coils of adjacent basic pairs, by interconnecting:

a. the outer ends of the second radial portions of the first coil sections of the second and first coils of adjacent basic pairs, and

b. the outer ends of the first radial portions of the the second and first coil sections of the section and first pancake coils of adjacent basic pairs. 

1. An interleaved turn, high series capacitance winding for electrical inductive apparatus, comprising: a plurality of pancake coils disposed in spaced, side-by-side relation, each of said pancake coils including first and second insulated conductive strands spirally wound together to provide first and second radially interleaved coil sections, the first and second coil sections of each of said pancake coils each being severed to provide first and second radial portions, each having inner and outer radially spaced ends, first means interconnecting said plurality of pancake coils into a plurality of basic pairs, having first and second paths through each basic pair, with the paths spiralling inwardly in a first circumferential direction in the first coil of a basic pair, and outwardly in the same circumferential direction in the second coil of a basic pair, said first means interconnecting the coils of a basic pair such that the turns of the first and second paths are mutually interleaved in the first coil, and the turns of the first and second paths are each self-interleaved in the second coil of the basic pair, and second means interconnecting the paths of the adjacent basic pairs to continue the first and second paths through the winding.
 2. The winding of claim 1 wherein the second means interconnects the adjacent basic pairs such that the relative positions of the first and second paths are interchanged from basic pair to basic pair.
 3. The winding of claim 1 wherein the first and second paths through the winding are interconnected, at least at the ends of the winding.
 4. The winding of claim 1 wherein the first means interconnects, in each basic pair, a. the outer ends of the second radial portions of the second coil sections of the first and second pancake coils, b. the inner ends of the second radial portions of the second and first coil sections of the first and second pancake coils, respectively, c. the inner ends of the second and first radial portions of the first section of the first and second pancake coils, respectively, d. the outer ends of the first radial portions of the second and first sections of the first and second pancake coils, respectively, e. the inner ends of the first radial portions of the second sections of the first and second pancake coils, and f. the inner ends of the first and second radial portions of the first and second coil sections of the first and second pancake coils, respectively.
 5. The winding of claim 4 wherein the second means interconnects adjacent coils of adjacent basic pairs, by interconnecting: a. the outer ends of the second radial portions of the first coil sections of the second and first coils of adjacent basic pairs, and b. the outer ends of the first radial portions of the the second and first coil sections of the section and first pancake coils of adjacent basic pairs. 